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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

ALASKAN GLACIER STUDIES
CHAPTER I THE GLACIERS OF ALASKA
The Alaskan glaciers are the largest in the world except those in polar regions.
The existing glaciers of Alaska are chiefly confined to the mountain regions and extend more or less continuously through about 1,100 miles along the Coast and the St. Elias Ranges, 400 miles in the Alaska Range, and 450 miles in the Endicott Mountains of northern Alaska. These mountain, snowfield, and glacier belts average from 40 to 120 miles in width. There are also scattered glaciers upon volcanoes through a distance of 500 miles on the Alaska Peninsula and Aleutian Islands. Glaciers are found through a range of 15 degrees of latitude. The total snow- and ice-covered area has been conservatively estimated at 15,000 to 20,000 square miles,1 and is much smaller than the area covered at the maximum stage of Alaskan glaciation. This, however, is less than four per cent of the total area of Alaska. There are thousands of glaciers, only a few hundred of which have been named.
The glacial districts in Alaska may be best described in groups associated with the various mountain ranges (Map 1, in pocket), both because these enable us to take up compact units, and because the mountains are jointly responsible with the climatic conditions for the existing glaciation. It is the combination of lofty mountains facing a sea coast where warm, humid, onshore winds bring abundant moisture, in a northerly latitude, that gives the Pacific Mountains of Alaska from 80 to 300 inches of precipitation yearly. It is the loftiness of these mountains, and the northerly latitude, that causes a large proportion of this precipitation to fall in the form of snow. Therefore, much more snow falls in a winter than can melt during a summer, causing permanent snowfields and great glaciers. The variations in altitude, in latitude, in precipitation, and in direction of slope cause the principal variations in the present size and condition of the glaciers. Most of these variations are associated with differences in the mountains, but it is not certain that the climate is responsible for all the glacial oscillations, nor that the ice tongues are consistently waning.
The mountain ranges upon whose slopes most of the glaciers have been formed are the Pacific Mountains, including the various subdivisions of (1) the Canadian Coast Range, (2) the St. Elias Range, (3) the Alaska-Aleutian Ranges.
Former glaciation will be discussed in connection with all these mountain groups after the existing glaciation has been sketched.
Along the Inside Passage the Taku and Davidson Glaciers are rather familiar, as are the Muir Glacier of Glacier Bay, the Malaspina and Yakutat Bay Glaciers of the south side of the St. Elias Range, and the Valdez and Columbia Glaciers of Prince William Sound; but most of the other glaciers of Alaska are little known.
i Gilbert, G. K., Hamman Alaska Expedition, Vol. HI, 1904, p. 9; Nat Geog. Mag., Vol. XV, 1904, p. 450.
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